Thermal transfer ribbon cassette system

ABSTRACT

A thermal transfer ribbon cassette system for use with a thermal transfer printer comprises supply and take-up spools, a thermal transfer ribbon extending between the spools with one end loaded onto the supply spool and the other onto the take-up spool, a cassette casing (10) with spool-locating means (15, 16) to locate and retain the two ribbon-carrying spools (5) spaced-apart, parallel and rotatable during printing, the spacing between the spools being predetermined to fit the printer, and a disposable loading member (20) comprising a rigid body portion (21) shaped to be manually transportable and having spool-holding means (23) releasably to hold the loaded spools (5) parallel, non-rotatable and spaced apart with the same predetermined spacing as the spool-locating means (15, 16); the spools (5), casing (10) and loading member (20) being adapted to enable the spools (5) to be inserted into the spool-locating means (15, 16) of the casing (10) while being held by the loading member (20), and to enable the loading member (20) thereafter to be withdrawn while the spools (5) are retained in the casing (10).

FIELD OF THE INVENTION

The invention relates to thermal transfer printing, and in particular tomeans for holding the thermal transfer ribbons during storage and duringuse in thermal transfer printers.

BACKGROUND OF THE INVENTION

Thermal transfer printing is a process for generating printed images bytransferring thermally transferable colorant from a thermal transferribbon to a receiver. The ribbon usually comprises a base sheet coatedon one side with a transfer coat comprising a non-transferable bindercontaining one or more thermally transferable dyes, or a fusible inkwhich is all transferable. Printing is effected while the transfer coatis held against the surface of the receiver, by heating selected areasof the ribbon so as to transfer the dyes or inks from those selectedareas to corresponding areas of the receiver. This generates an imageaccording to the areas selected. By repeating the transfer process witheach of the three primary colours, full colour images can be obtained.Black may also be used.

Thermal transfer printers using a thermal head with a plurality of tinyheaters to heat the selected areas, have been gaining widespreadattention in recent years, mainly because of its ease of operation inwhich the areas to be heated can be selected by electronic control ofthe heaters (e.g. according to a video or computer-generated signal),and because of the clear, high resolution images which can be obtainedin this manner. Alternative thermal energy sources, such as addressablelaser systems, are also being developed.

Transfer sheets for such primers are normally in the form of longribbons, having repeated sequences of print size panels of each primarycolour and any other materials to be transferred (e.g. black dyes orink), such sequence being repeated along the ribbon to enable it to beused for as many prints as there are repeats of the sequence. Theribbons are rolled up and stored in a cassette. These consistessentially of supply and take-up spools, the thermal transfer ribbonextending between the spools with one end loaded onto the supply spooland the other onto the take-up spool, and a casing having spool-locatingmeans to locate and retain the spools spaced apart, parallel androtatable during printing with the spacing between the spools beingpredetermined to fit the printer. The cassettes may also be suppliedwith a small anti-rotation member which is plugged into the ends of thespools to prevent their rotation during transit to the consumer.

Cassette casings typically comprise two parallel spool-housings havingend portions interconnected by bridge members such that the housings andbridge members together define an open access port through which thetransfer ribbon is exposed as it extends from one spool to the other.However, there is at present no overall industry standard for thermaltransfer printers and cassettes, and the specific configurations of thelatter are largely determined by the printers with which they are to beused, both in respect of the overall shape and size (e.g. they must fitcorrectly into the space provided), and also in respect of thefunctional requirements (e.g. they must meet the requirements of varioussensors normally built into the printer). There may also be differencesbetween cassettes for printers using thermal heads to effect transferand those which are laser driven.

Such casings can represent a substantial proportion of the cost of thecassette, but after all the transfer ribbon has been used up, they areusually discarded. However, some known cassettes do have an openconfiguration which leaves the spools and their spent transfer ribbonsaccessible for replacement. Such replacement may be facilitated bypermitting longitudinal movement of the spools in the casing from a freeto a retained position, and some form of spring, e.g. leaf springs orcoil springs around the spool ends, provided to bias the spools intotheir retained positions.

Unfortunately, ribbon replacement is not without its difficulties. Thecolorants used in the ribbons are intended to be readily transferred toa receiver on application of heat, and when handled some of the colorantmay become similarly transferred to the hands or clothing. Moreover thetransfer sheet can itself become damaged by such handling, even when nocolorant is actually transferred. Particularly susceptible to this aretransfer coats comprising thermally transferable dyes held in a staticbinder from which they diffuse during printing, because such dyes aregenerally soluble in finger grease. Where the transfer coats arehandled, any grease deposited may cause such dyes to diffuse to thesurface where they accumulate and form crystals. These make the transfersheets even more dirty, and may produce noticeable unevenness in a printmade from that part of the transfer sheet.

SUMMARY OF THE INVENTION

We have now invented a cassette system wherein the ribbon can moreeasily be replaced with a new refill without contact between thetransfer coat and the operator's hands, and the refill can be packagedin a form ready to be inserted into the casing by the consumer.

According to a first aspect of the present invention there is provided athermal transfer ribbon cassette system for use with a thermal transferprinter, the system comprising supply and take-up spools, a thermaltransfer ribbon extending between the spools with one end loaded ontothe supply spool and the other onto the take-up spool, and a cassettecasing with spool-locating means to locate and retain the tworibbon-carrying spools spaced-apart, parallel and rotatable duringprinting, the spacing between the spools being predetermined to fit theprinter; the system also including a disposable loading membercomprising a rigid body portion shaped to be manually transportable andhaving spool-holding means releasably to hold the loaded spoolsparallel, non-rotatable and spaced apart with the same predeterminedspacing as the spool-locating means; the spools, casing and loadingmember being adapted to enable the spools to be inserted into thespool-locating means of the casing while being held by the loadingmember, and to enable the loading member thereafter to be withdrawnwhile the spools are retained in the casing.

A purpose of the loading member is to enable an operator to hold arefill manually by the loading member rather than by the loaded spools.Consequently these need to shaped to be manually transportable, but suchshaping can be minimal provided the function is available. Thus forexample, the body may be moulded with an integral handle, which providesan economical way of shaping the body portion to be comfortable to holdand transport manually, with the advantage of improved rigidity; butthere are also suitable alternatives, including forming an integralflange around part or all the periphery of the body portion to give abroader edge that can be gripped twixt finger and thumb, for example. Inextreme cases the body may be moulded with sufficient thickness toenable it to be gripped without such peripheral flanges, eg by having afoamed core, but this may not be the most economical way to providemanual transportability.

Supply and take-up spools typically have two end portions located eitherside of a bobbin portion onto which the respective ends of the thermaltransfer ribbon are loaded, with one corresponding end portion of eachspool being hollow by way of having an axial cavity for engaging drivingmeans in the printer. The spool-holding means of the loading member canthen comprise two parallel spaced-apart rods extending orthogonally fromthe body portion to fit securely but releasably in the respectivecavities. The simplest way of gripping the spools is then for the rodsto have extended end portions which are an interference fit in therespective cavities. The lengths of the rods and cavity depths need onlyto be sufficient to hold the loaded spools parallel as they extend fromthe body portion. When the rods are pushed home sufficiently to supportthe spools, they can also prevent rotation of the spindles duringtransit, and can be withdrawn after the refill has been located in thecasing, simply by overcoming the friction of the interference fit.

A preferred cassette system is one wherein each spool-locating means forlocating and retaining the hollow end portion of a spool comprises twoarcuate upstands forming a major portion of an incomplete retaining ringwith a gap between the ends of the upstands which is less than theexternal diameter of the hollow end portion of the spool, and each ofthe rods has at least a portion with a smaller diameter than the spool,being less than the width of the gap, and wherein the retaining ringsare of a size to receive the hollow end portions with freedom for thespools and rods to move axially between a free position in which thesmaller diameter portion is aligned with the gap to enable it to passtherethrough, and a retained position in which the hollow end portion isaligned with the gap to prevent the spool passing therethrough, wherebythe spools held on the holding means can be inserted into the freeposition within the cassette by passing the rods through the gaps, thenmoved axially into the retained position and the holding means separatedand removed. The casing suitably contains means to bias the spools fromthe free position into the retained position, thereby to maintain thespools in the retained position after removal of the spool-holdingmeans.

Each of the rods with a diameter which provides an interference fit inthe spool cavity, suitably has the diameter which is less than the widthof the gap provided as a reduced diameter in just an intermediateportion of the rod. This gives a waisted shape, as produced, forexample, by a circumferential groove, but depending on the method ofconstruction, we find it is often simpler to reduce the diameter of theintermediate portion of the rod in one diametric direction only, by theprovision of a slot on each side of the rod.

According to a second aspect of the present invention there is provideda refill unit for a thermal transfer ribbon cassette having a casingwith spool-locating means to locate and releasably secure tworibbon-carrying spools spaced-apart, parallel and rotatable duringprinting, the refill unit comprising supply and take-up spools having athermal transfer ribbon loaded onto and extending between them, and adisposable loading member comprising a rigid body portion shaped to bemanually transportable and having spaced spool-holding means holding theloaded spools and maintaining them parallel, non-rotatable and spacedapart with the same predetermined spacing as the spool-locating means,said loading means being releasable from the spools after the latterhave been loaded into and are retained by the spool-locating means.

According to a third aspect of the present invention, a method ofrefilling a thermal transfer cassette having a casing with spacedspool-locating means, comprises the steps of loading a thermal transferribbon onto a pair of spools, providing a loading member comprising arigid body having spaced means for holding the loaded spools, engagingthe spool-holding means and the spools so that the latter are heldparallel, non-rotatable and spaced apart with the same spacing as thespool-locating means, inserting the spools into the casing while held bythe loading member, thereafter allowing or causing relative movementbetween the casing and the spools until the spools are held by thespool-locating means, releasing the spools from the loading member andwithdrawing the latter leaving the loaded spools retained in the casing.

The cassette system and refill unit of the present invention provide anumber of advantages over previously known cassettes and refill methods.In particular it reduces the amount of wasted material and expense byenabling discarded mouldings to be limited to a minimal loading member,rather than a full cassette casing. This frees the cassette designer toproduce a cassette with optimum performance characteristics, such asincluding reinforcement to give optimum rigidity, without commercialconstraints of minimising the cost of mouldings discarded with the usedribbons. Compared with other refillable systems, the provision of theloading member enables a non-technical consumer to perform the refillingact without risk of damaging the ribbon or soiling their hands orclothes, because all that needs to be handled is the loading member.

As may have been noted from the above discussions of the prior art,cassettes have previously been supplied with small disposableanti-rotation devices which plugged into the ends of the spools toprevent their rotation during transit to the consumer. However, thesewere employed with filled cassettes, rather than refills, and were notsuitable for use with those cassettes as a loading member according tothe present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

To illustrate the invention, a specific embodiment thereof is shown inthe accompanying drawings, in which: FIG. 1 is an exploded perspectiveview of a cassette system according to the invention, showing a refill,casing and loading member all separate. FIG. 2 is a view similar to thatof FIG. 1, except that the refill is held by the loading member, FIG. 3is a similar view to the above, with the refill inserted into the casingwhile held on the loading member, and FIG. 4 is a similar view whereinthe loading member has been withdrawn from the refill. Like referencenumerals having been used for like parts in all four drawings.

DETAILED DESCRIPTION OF THE INVENTION

The refill 1 comprises two spools each having a broad spindle portion 3at one end and a narrower spindle portion 4 at the other. Between thetwo spindle portions are bobbin portions (obscured) on which are wound adyesheet ribbon 5. Between the broad spindle portion 3 and the bobbinportion is provided a circumferential flange 6. The broad spindleportions are hollow, having an axial printer-drive-receiving cavity 7with internal knurls for engaging driving means in the printer.

The casing 10 comprises two parallel spool-housings 11, having endportions interconnected by bridge members 12 and 13, such that thehousings and bridge members together define an open access port 14. Ateach end of the housings are first and second spool-locating means 15and 16 to receive corresponding end portions of the spools with freedomto move longitudinally between a free position as shown in FIG. 3, and aretained position as shown in FIG. 4. Each first spool-locating means 15comprises a box with a spindle-receiving hole 17 and containing springmeans (not shown) to bias the spools into the retained position, andeach second locating means 16 comprises two arcuate upstands to form amajor portion of an incomplete retaining ring 18, with a gap 19 betweenthe ends of the upstands. The hole 17 and ring 18 are sized to providebearings in which the respective spindle portions of the spools can berotatably mounted, and to provide retaining means to retain the spindleportions in the bearings when the spools are in the retained positions.

The loading member b comprises a rigid body portion 21 having anintegral handle 22, and two spool-holding means. The latter are parallelrods 23 extending from the rigid body portion 21, each with taperedextended ends 24 and a waisted portion 25 formed by a recess on bothsides only one of which can be shown on each rod). The rods 23 are afirm interference fit in the cavities 7 of the broad spindle portions 3at one end of the spools. The integral handle provides an economical wayof shaping the body portion to be comfortable to hold and transportmanually, and improve the rigidity at the same time.

The refill unit is first assembled by combining the refill 1 and theloading member 20, as shown in FIG. 2. To achieve this the taperedextended ends 24 of rods 23 on the loading member, are pressed into thecavities 7 of the refill, up to but not including the waisted portion 25of the rods. The interference fit between the rods 23 and the knurls inthe cavity 7 provides the loading member with a good non-rotatable holdon the refill, whilst keeping the spools spaced apart and parallel. Therefill unit can then readily be picked up and transported manually byusing the handle 22, with little danger of the user inadvertentlytouching the spooled ribbon.

The refill unit is inserted into the casing as shown by guide lines 30in FIG. 2. First the narrow spindle portions 4 are inserted into theholes 17 until resistance by the spring means in the boxes 15 is felt,and then continued until the waisted portions 25 of the rods 23 becomeadjacent to the gaps 19. The loading member is then lowered through thegaps so that those waisted portions enter into the rings 18 of thesecond bearings as shown in FIG. 3. This is the "free position" referredto above, in which the spindles are still free to be lifted out of theretaining rings 18 and removed.

On withdrawing the loading member from the hollow ends of the spools (asindicated by the arrow 31 in FIG. 4), bias from the spring means causeslongitudinal movement of the refill spools in the casing from the freeposition shown in FIG. 3, until the flanges 6 contact the rings 18, andprevent further movement. In so moving the refill unit, the gaps 19 inthe second bearing portions 16 come into alignment with the broaderspindle ends of the spools 3 (instead of the waisted portions of theloading member rods), which are not able to pass back out through thegaps 19, thus retaining the refill in place. Hence this is the "retainedposition" referred to above, and is shown in FIG. 4.

The loading member thereafter plays no active role in the operation ofthe refilled cassette during printing, and may be discarded or recycledas part of a fresh refill unit, as desired. Being a smaller, simplermoulding than the cassette, whether the loading member is discarded orrecycled, this represents an environmentally more friendly option thandoing the same with the full cassette, and is a more user-friendly wayof refilling the cassette than handling the refills directly.

I claim:
 1. A thermal transfer ribbon cassette system for use with athermal transfer printer, comprising:supply and take-up spools, eachhaving a corresponding end portion which is hollow with an axial cavityfor engaging driving means in the printer; a thermal transfer ribbonextending between the spools, with one end loaded onto the supply spooland the other onto the take-up spool; a cassette casing withspool-locating means to locate and retain the two ribbon-carrying spoolsspaced-apart, parallel and rotatable during printing, the spacingbetween the spools being predetermined to fit the printer; and adisposable loading member to hold the spools parallel, spaced apart andnon-rotatable while they are being inserted into the spool-locatingmeans of the casing; wherein the loading member comprises a rigid bodyportion shaped to be manually transportable, and two parallelspaced-apart rods extending orthogonally from the body portion withextended end portions to fit securely but releasably in the respectivespool cavities; the spool-locating means for locating the hollow ends ofthe spools, each comprises two arcuate upstands forming a major portionof an incomplete retaining ring, with a gap between the ends of theupstands which is less than the external diameter of the hollow endportion of the spool but greater than the diameter of at least anintermediate portion of the rod; the retaining rings are of a size toreceive the hollow end portions with freedom for the spools and rods tomove axially between a free position in which the intermediate portionof the rod is aligned with the gap to enable it to pass therethrough,and a retained position in which the hollow end portion is aligned withthe gap to prevent the spool passing therethrough; whereby the tworibbon-loaded spools can be inserted into the cassette by holding thespools on the extended end portions of the rods, inserting the spoolsinto the free position within the cassette by passing the intermediateportions of the rods through the gaps, moving the spools axially intotheir retained positions, and withdrawing the loading member from thespools while the latter are retained in the casing.
 2. A cassette systemas claimed in claim 1, wherein the extended end portions of the rods arean interference fit in the respective cavities.
 3. A cassette system asclaimed in claim 1, wherein the casing contains means to bias the spoolsfrom their free positions into their retained positions.
 4. A cassettesystem as claimed in claim 1, wherein the diameter of the rod which isless than the width of the gap, is a reduced diameter provided in justthe intermediate portion of the rod.
 5. A cassette system as claimed inclaim 4, wherein the diameter of the intermediate portion of the rod isreduced in one diametric direction only, by the provision of a slot oneach side of the rod.
 6. A refill unit for a thermal transfer ribboncassette, wherein the refill unit and the cassette together form acassette system as claimed in any one of claims 1 to 5, and wherein therefill unit comprises the supply and take-up spools with their axialcavities, the thermal transfer ribbon extending between the spools, andthe disposable loading member with its rods fitted securely butreleasably in the respective spool cavities to hold the spools parallel,non-rotatable and spaced apart, wherein said spools each have a broadspindle portion at one end and a narrower spindle portion at the other.